The invention relates to a correction system for a high resolution charged-particle beam apparatus provided with a first and a second hexapole enclosing a round lens system.
Such a correction system is known from U.S. Pat. No. 4,414,474. A hexapole corrector described in U.S. Pat. No. 4,414,474 is dedicated to correct third-order spherical aberration particularly in a scanning transmission electron microscope (STEM). This corrector is free of axial aberrations only. Owing to the non-vanishing second order off-axial aberrations, these correctors result in a relatively small field of view. Due to the use of a single magnetic lens between the hexapoles, this corrector causes a fourth-order aperture aberration preventing an appreciable improvement in resolution in optical systems having a relatively wide field of view such as a transmission electron microscope.